The wrist (carpus) is composed of 8 bones (carpals). All of these bones are vulnerable to injury following direct trauma. The scaphoid however, is the most commonly injured bone of the carpals, accounting for 60-70% of all carpal fractures. It is most commonly injured with a fall on an outstretched arm. In many sports such as rollerblading, skating, snowboarding, mountain biking and skiing this is a common mechanism of injury. In addition, the scaphoid may face complications during healing due to its unique anatomy.
The scaphoid is located on the thumb (lateral) side of the wrist and functions to link the radius of the forearm with the thumb, index and ring fingers of the hand. The scaphoid is bound to the radius and 4 other wrist bones by a complex ligament system. It functions in all movements of the wrist and is most vulnerable in a position of wrist extension (as in pushing up from a chair). The scaphoid is particularly involved with movements of the thumb and index fingers, which are essential for gripping activities and fine motor control. The scaphoid receives its blood supply from the radial artery. Unlike most bones, the scaphoid receives its oxygenated blood from its distal (furthest) end. The blood then must travel backwards to supply the proximal (nearest) end of the bone. It is this unique blood supply that often makes healing of scaphoid fractures difficult.
When wrist extension is combined with a fall onto the hand, or direct trauma to the wrist/scaphoid, ligament sprains or wrist fractures can occur. If the scaphoid is fractured, early detection and monitoring is essential to proper healing. These fractures can be diagnosed by wrist x-ray. Conventional wrist x-rays may not show a fracture, and therefore it may be necessary for specific x-rays of the scaphoid at various angles. Occasionally these fractures may still be missed, and follow-up x-rays are sometimes required if healing doesn’t proceed as expected. Alternatively, further examinations such as bone scan, CT scan or MRI may be used. If the fracture fails to unite, the blood supply to the proximal end of the bone may be compromised. This can result in decay of the bone from lack of oxygenation and mineralization, a condition known as avascular necrosis. Factors that may indicate a poor prognosis include late diagnosis, location and displacement of the fracture.
Treatment depends on the extent of the injury. If the scaphoid is fractured, the management will be more conservative than if the wrist is sprained. For fractures, the treatment is dependent on the type and extent of fracture.
Undisplaced, Stable Scaphoid Fractures
This means the broken parts of the bone are in close proximity to each other, and there is no movement of the bony ends. Prognosis is excellent in these cases. The thumb and wrist will be immobilized for a period of 4-6 weeks, typically with a wrist and thumb splint. X-rays are taken at 6 weeks, and if union is delayed, continued immobilization will be necessary.
Displaced, Unstable Fractures
This means the broken ends of the bone are not in even contact with each other and may be free to move around. The bones may need to be “repositioned” by an orthopaedic specialist and then immobilized through splinting and/or casting. In these cases, surgical intervention may be warranted.
In any case, if healing is delayed and the fractured ends do not unite, surgical intervention may still be necessary.
Non-Union of Scaphoid Fractures
Influenced by delayed diagnosis, severe displacement/dislocation, more proximal fractures (impaired blood supply), and associated carpus injuries. Many non-unions display minimal symptoms and can be tolerated well in the low demand wrist (older age, sedentary lifestyle.) Degenerative arthritic changes are probably inevitable, but may not occur for years.
Salvage procedures are generally reserved for painful non-unions. These include excision of small fragments, styloidectomy (more commonly used as a source for bone graft and to improve exposure), interposition of a dorsal soft tissue flap to create a painless pseudoarthrosis (Bentzon’s Procedure), vascularized radial graft, proximal row carpectomy, silicone implant arthroplasty, and partial or total arthrodesis of the wrist